1. Field of the Invention
The present invention is generally directed to vehicular suspension systems, and in particular to suspension systems incorporating roll stabilisation mechanisms.
2. Description of the Background Art
Modem vehicles are normally provided with one or more roll stabilisation or "torsion" bars which transversely link the wheels of one or more axles in order to afford some containment of roll motion to prevent uncomfortable and sometimes dangerous swaying motions when cornering. Roll stabiliser bars are typically manufactured as spring steel bars which permit torsional resilience so that as one wheel on an axle is caused to move in a generally upward or downward direction the other wheel on the same axle is induced to move in a similar direction at the same time. The extent to which the two wheels of a single axle move in a common direction is defined in part by the torsional rigidity of the roll stabiliser bar which transversely couples the two wheels in response to the lateral roll force exerted on the vehicle resulting from cornering.
Vehicles with high centres of gravity (such as trucks which are prone to excessive roll motions) and vehicles which are required to `corner flat` without exhibiting excessive roll motions (such as sports cars) are normally provided with stiff roll stabiliser bars to prevent roll motion. An unbeneficial consequence of providing stiffer roll stabilisers is that the ride quality becomes harsher as both wheels of an axle become functionally linked (to an extent) and single wheel inputs are therefore not resolved by that single wheel alone which impacts on a bump or pot-hole.
Luxury passenger vehicles are, therefore, normally equipped with more compliant roll stabiliser bars so that single wheel inputs are absorbed by that single wheel's associated spring and damper unit which are relatively free to move in response to the single input without the additional resistance resulting from the stabiliser's torsional rigidity.
Regardless of the torsional rigidity of the torsion bar, the provision of such bars do restrict the degree of movement of the wheels relative to each other. This can be a disadvantage in situations where a large degree of opposing vertical wheel motion is required, for example, when travelling over undulating surfaces. The limitations of the wheel movement due to the roll stabiliser bars interconnecting the wheels can lead to significant side to side jerking of the vehicle under such conditions. This movement limitation also restricts the amount of traction that the wheels will have when travelling over such surfaces.
When travelling over uneven ground, the points where the wheels contact the ground are not all in a single plane. This results in the suspension of two diagonally opposed wheels becoming compressed, with the wheels moving closer to the vehicle body, and the suspension of the other two diagonally opposed wheels becoming extended. This mode of suspension operation is known as `warp` or alternatively `cross-axle articulation`.
It would be advantageous to have a vehicular suspension system which provides roll stability during cornering and also provides a comfortable ride when travelling in a near straight line or when traversing an undulating surface.